1. Field of the Invention
The present invention relates in general to an in-line filter device connected to a compressed air line, and more particularly to such an in-line compressed air filter device having an improved structural arrangement, which is capable of efficiently preventing retaking or re-evaporation of trapped or separated liquid particles such as water and oil which have been contained in a compressed air stream, and which assures improved efficiency of removal of the liquid particles from the compressed air line.
2. Discussion of the Prior Art
Conduits used for supplying compressed air to various pneumatically operated components employed in various factories, atomic plants and medical equipment, for example, are generally provided with an in-line filter device or vapor trap assembly for removing water and/or oil vapor contained in a stream of compressed air, for the purpose of protecting the pneumatic components or improving the performance of those components.
A type of such an in-line filter device for compressed air, which minimizes vapor and/or liquid particles contained in the compressed air, has been disclosed in U.S. Pat. No. 4,487,618 to David O. Mann. The disclosed filter device includes first filter means having a suitable first packing inside a sleeve thereof, and second filter means having a suitable second packing inside a sleeve thereof. The first and second filter means are disposed parallel with each other, so as to extend in the vertical direction from an air-tightly enclosed trap structure having a suitable volume capacity, such that each of the first and second filter means communicates with an enclosed volume or trap chamber formed within the trap structure. The compressed air is directed to the trap chamber through the first filter means from an intake conduit, so that vapor (oil vapor) and/or liquid particles contained in the compressed air are condensed or coalesced into droplets, whereby the vapor and/or liquid particles are separated from the compressed air, and the droplets are captured within the trap chamber. Subsequently the compressed air from which the vapor and/or liquid particles have been separated is directed to an outlet conduit through the second filter means from the trap chamber, so that any remaining liquid particles are vaporized. Thus, the amount of the vapor and/or liquid particles entrained in the air entering the outlet conduit is minimized.
In the in-line filter device as described above, the liquid separated from the compressed air should be efficiently discharged from the filter device, without lowering the pressure of the air flowing through the filter device. For this purpose, a drain hole which is provided at the bottom portion of the trap chamber is suitably provided with a drain valve as disclosed in laid-open Publication No. 45-36182 of examined Japanese Patent Application (corresponding to U.S. Pat. No. 3,418,789) or other suitable draining means. The drain valve disclosed in the above publication is automatically opened to discharge the trapped liquid (collected droplets) when the liquid is accumulated to a predetermined volume.
In the filter device wherein the trapped droplets are discharged by means of such a drain valve, however, the liquid always stays in a given amount in the bottom space of the filter device. Thus, the liquid tends to be re-taken by the compressed air flowing through the trap chamber or tends to be re-vaporized, so that the liquid is returned into the compressed air stream, whereby the efficiency of removal of the liquid particles from the compressed air is lowered.